1. Field of the Invention
The present invention concerns a positioning system, positioning method, and positioning device to measure the current position of the device.
2. Background of the Invention
Recently, it became possible to use artificial satellites for navigation, and a GPS (Global Positioning System) that makes navigation possible not only for ships but also for cars and people when suitable devices are carried with them has been offered. Economy, safety, and convenience, while travelling towards a destination, are improved by this navigation system.
In addition, in the GPS, positioning errors are corrected and positioning accuracy is improved by making use of a relative positioning method (differential GPS or DGPS). In general, in a differential GPS, positioning errors are corrected by sending out correction data to a GPS receiver from a transmitting station using FM-multiplex broadcasting.
However, a navigation system using FM-multiplex broadcasting with a differential GPS has the problem described below.
First of all, since FM-multiplex broadcasting uses a bandwidth around 80 MHz, it becomes necessary to lengthen the antenna, which is a disadvantage from the standpoint of portability.
Also, since one broadcasting station covers a very wide area, there is a limit to the correction of positioning errors.
In addition, GPS's reception sensitivity is not good underground or inside a building. In general, it cannot receive FM-multiplex data when located underground or inside a building.
When using FM-multiplex broadcasting, the electric power needed at the receiving terminal is large, which is a disadvantage from the standpoint of portability. For example, one had to have large capacity batteries, which was a problem.